Field of the Invention
The invention relates to a protective cover and, more particularly, to a protective cover and a protective cover set with a wireless charging function.
Description of the Related Art
As wireless charging technology becomes popular, it is widely applied to electronic devices, such as a smart phone, a video player or a camera. The safety regulation and compatibility between different systems should be taken into consideration when a charging device provides stable and high power to the electronic device.
Conventional wireless charging system includes at least one transmitting end and one receiving end. Both the transmitting end and the receiving end include a coil. Alternative current is provided via the transmitting end, the receiving end collects the near-field inducting power, and a rectifier and a voltage adjusting circuit are used to convert the alternative current to direct current. In order to control the power transmission, the receiver should communicate with the transmitter continuously to inform the required power, electric quantity and a timing of stop power transmission.
Moreover, if a metal object exists between the transmitting end and the receiving end in the power transmission process, the metal object is heated by the electromagnetic waves from the transmitting end. Thus, the metal object may scorch the user or damage the electronic device. In order to solve the problem, a wireless charging system usually includes a foreign object detection (FOD) function. It can detect whether a metal object exists between the transmitting end and the receiving end by calculating the power loss between the transmitting end and the receiving end. If the power loss is larger than a predetermined value, it can be determined that a metal object exists between the transmitting end and the receiving end, and when the temperature of the metal object exceeds a predetermined temperature due to the power absorbed by the metal object, the transmitting end stops providing power.
Most electronic devices include metal components, but the metal components would cause power loss. In order to avoid the misjudgment due to those metal components, an FOD adjusting value is usually matched with a resistance to ground as a power compensation value to offset the power loss caused by the metal components of the electronic device. However, different electronic devices have different compensation values. That means, an electronic device with a wireless charging function can only charge itself, which is rather inconvenient.